H.323

In order to communicate effectively, a common language between the two (or more) participants must be chosen. Without a common language, there will be little or no understanding, resulting in a passing of merely "noise" between the parties. This doesn't apply only to people; computers particularly must have common ground when communicating to one another, notably because of the context-free world in which they operate.

Networks of computers, therefore, are built on standards and protocols, selected so applications that are dependent upon the network can exist and operate at their fullest capabilities. There are several notable organizations that work to develop standards, both formal and ad hoc, across a variety of fields. The ITU (International Telecommunications Union) is one such organization, a prominent group that develops internationally recognized recommendations and standards to enable computers, radios, and other machines to interact with one another.

The ITU H.32x family of standards handles multimedia communications. This family includes H.320 (communication over ISDN [integrated services digital networks]) and H.324 (communication over SCN [switched circuit network], better known as traditional phone services).

H.323 is a communication standard produced by the ITU, initiated in late 1996, and aimed at the emerging area of multimedia communication over LAN's (local area networks). It is an outgrowth of the traditional H.320 technology but optimized instead for the Internet. H.323 has since been revised to include voice-over IP and IP telephony, as well as gatekeeper-to-gatekeeper communications and other data communications that involve packet-based networks. These networks include IP-based networks like the Internet, Internet Packet Exchange (IPX) LAN's, and WAN's. H.323 is widely supported by many commercial vendors and used throughout the world in commercial and educational markets.

The H.323 standard specifies a great deal of information about the properties and components that interact within an H.323 environment. It specifies the pieces that combine to provide a complete communication service:

• terminals, either PC or stand alone devices, these are the endpoints of the communication lines
• gatekeepers, the brains of the network; providing services like addressing/identification, authorization, and bandwidth management
• gateways, which serve as translators when connecting to a dissimilar network (such as an H.324, for example)
• MCU's (multipoint control units) which allow multipoint conferencing, or communication between more than two parties at once (much like a traditional conference call on a telephone)

In addition to component types, H.323 also describes protocol standards, permissible audio and video codecs, RAS (registration, admission, and status), call signaling, and control signaling. H.323 specifies a mandatory level of compliance and support for the above specifications for all terminals on the network. More detailed information about H.323 is available through several links shown in the appendices.

Hardware Assist

In most videoconferencing over IP, including H.323, the endpoints compress the audio and video data to be exchanged so that transmission of that data over the network will be less likely to degrade and will consume less network bandwidth. The trade-off for this added network efficiency is a need to compress the media stream as it leaves the sending endpoint and then decompress the media (audio/video) stream for interpretation once it arrives at the receiving endpoint. This compression and decompression require processing power and additional time. The less processing power there is, the more delay is introduced into the communication.

H.323 videoconferencing is often considered a desktop technology but PCs in general are not yet powerful enough to do high-quality full-screen, full-motion video compression and decompression, especially in addition to all the other applications that a PC might be running at the same time a videoconference is desired. This has forced leading H.323 vendors to integrate hardware-based codecs ("compressor/decompressor") into their videoconferencing products. These codecs are specifically designed to offload the compression and decompression task from the PC, allowing the endpoint overall to achieve good performance. In the past and often still today, the codec is included as an additional PCI bus card in the PC. These and similar PC products can support a high frame rate (15 - 30 frames per second) and extended range of call quality/bandwidth settings (128K - 1.5Mb) so that videoconference quality seen at one's desktop can equal that of larger and more expensive room-based conferencing systems. Examples of this include the Zydacron OnWAN and the VCON Escort series.

More recently, the trend is toward "plug and play" external devices that plug into a USB port. The extra processing power required for encoding is included in the USB camera/device with the USB port providing the "bandwidth" necessary for the compressed video to pass from the camera/device to the PC. Examples of this approach are Polycom's ViaVideo and the VCON ViGo.

Another addition to the "hardware line-up" of videoconferencing endpoints is the standalone non-PC-based "appliance". These appliances are specialized hardware devices (system/camera/microphone combinations that typically sit on top of a TV monitor) that provide high quality videoconferencing for medium to large conference rooms. They do not run other programs such as a PC-based endpoint might and they are larger and more expensive, yet often as simple or simpler to use as USB devices on a desktop PC.  The Polycom ViewStation and Tandberg 880 are examples of set-top H.323 appliances.

Overall, though hardware-based endpoints cost more than their software-only counter-parts (which range from inexpensive to free and are discussed in the following section), the extra cost is often justified in order to achieve videoconferencing call quality that is acceptable beyond just novelty or casual use.

Software Clients

Many vendors that have offered H.323 desktop hardware clients are now offering software based H.323 client. Software based clients are often cheap to implement due to the low cost of simple USB cameras and cheap microphones. And they are inexpensive (generally around $100-150), which makes a software-based solution quite appealing to organizations with little or no funding for videoconferencing. The caveat is that software clients require more powerful desktop systems to function well since they use the main system CPU to encode and decode video. In the past this has been a great burden on the system, often causing choppy video or other problems.  But, with the growing prevalence of the multi-gigahertz PCs and Macs, we are seeing good performance from these software clients. (See Tips for Selecting and Tuning your PC for software client requirements.)

VCON has introduced their vPoint software based client.  vPoint software can be used in conjunction with the VCON VIGO USB hardware client for accelerated video handling, or as standalone software with a standard USB or firewire camera. vPoint also incorporates H.239 for simultaneously sending and receiving video and data streams and supports encrypted conferences using the H.235 encryption standard. vPoint includes H.264 video compression. See VCON vPoint HD [21] for more information.

RadVision has recently introduced eConf. eConf Standard is available for either H.323 or SIP and runs to a maximum bandwidth of 384Kbps. eConf PPG provides dual protocol functionality (both H.323 and SIP) in one product and runs to a maximum bandwidth of 768 Kbps. eConf includes T.120 for data and application sharing. See RadVision eConf [22] for more information.

And Polycom now offers their PVX software client. PVX offers performance up to 2 Mbps, 30fps, H.264 video compression, AES encryption including H.235 v3 for interoperability across IP networks, multiple monitor support, and a graphical user interface in 11 languages. See Polycom PVX [23] for more information.

Open Source H.323

Open Source Software

The basic idea behind the open source movement is that when the source code for software is freely available, large numbers of programmers will read and evaluate that code. They will then make improvements and fix bugs more quickly than any company that is supporting similar proprietary code. Other major advantages of open source code include cost and portability. Free open source code can make software, such as H.323, available where money is an issue (and time less of an issue.) Open source code is portable in that it can often be compiled to run on different types of computers and different operating systems.

The Open Source Initiative [1] (OSI), a non-profit corporation that promotes open source software says "Open source promotes software reliability and quality by supporting independent peer review and rapid evolution of source code. To be OSI certified, the software must be distributed under a license that guarantees the right to read, redistribute, modify and use the software freely."

Open H.323

The OpenH323 project [2] aims to create a full featured, interoperable, Open Source implementation of the ITU H.323 teleconferencing protocol that can be used by personal developers and commercial users without charge. The OpenH.323 project is "coordinated" by QuickNet, an Australian manufacturer of hardware-based voice codecs for H.323.

The OpenH323 project includes:

It is difficult, of course, to know just how much OpenH.323 is being used - or any open source software, for that matter. One possible indication is that on SourceForge, the largest online depository of open source software, components of openH.323 are in the 96th percentile for "activity" (downloads, requests for support, postings, etc.). The Open h.323 GK is listed in the 90th percentile, for example.

GnomeMeeting

GnomeMeeting [3] is a GUI-based client for Linux. There is evidence of an active and stable GnomeMeeting development community.

GnomeMeeting was written by Damien Sandras as his final year project for his degree in Computer Science Engineering at Universite Catholique de Louvain Department of Computing Science and Engineering [4] in Louvain-La-Neuve.

This program allows Linux and FreeBSD users to videoconference with industry standard H.323 applications such as the Microsoft NetMeeting program for Windows. The program has proved extremely popular with users, and is now included in many Linux distributions as well as with FreeBSD.

GnomeMeeting Features: